Specifically, they want muskrat bellies, the felt-like fur that is practically impermeable to moisture. At $10 per pelt—five times what muskrats fetched in the 1990s—pelts were trading at new highs when bidding for last season's furs ended in June.

But some in the belly trade are casting worried glances at Europe, where fur sales are expected to be soft this winter. That could drag prices down for trappers here, and the current muskrat mania could prove to be a belly flop.

There's a lot for trappers to lose. High prices for the riparian rodents known as "the trapper's meal ticket"—or, simply, "rats"—have been good to trappers like Jay Keranen and his 8-year-old son, Jordan. The pair showed up with a dozen other men to the ice-covered parking lot of the Veterans of Foreign Wars post here Dec. 10 for an annual tradition: the fur pickup.

Stamping feet against the bitter cold, trappers came to deliver sacks of skinned muskrats to a buyer for one of Canada's leading wholesalers, Fur Harvesters Auction Inc. The North Bay, Ontario, company grades fur and sells pelts in lots to bidders.

The North American muskrat market has been booming, thanks to soaring fur sales in China and Russia. WSJ's Joel Millman reports from Calumet, Mich.

"I got 24 rats," declared Mr. Keranen, a self-employed contractor, as he pulled out a stack of flat skins, each about the size of a padded oven mitt. The collector, 66-year-old Al Niemala, who also traps himself, filled out receipts. Sporting a floppy muskrat hat and enormous muskrat gloves, Mr. Niemala took in about a hundred muskrats before driving to his next stop.

All told, Fur Harvesters collected 3,120 muskrats from Upper Peninsula trappers in December, and another 16,000 rats from trappers in Wisconsin, Iowa, Minnesota and the Dakotas.

Fur Harvesters Auction was one of three buyers sending circuit-riders through Michigan last month for muskrats. Stretched among 16 towns known as trapping centers, the pickup routes follow trails that buyers have worked for decades, linking the parking lots of taverns, some truck stops and a funeral parlor.

Michiganders love muskrats because the state imposes no limit on the number a trapper can take, which is not the case for otters, martens or bobcats. Moreover, the lowly muskrat is easy to catch and skin.

Furs of all kinds have staged a global comeback. Industry experts peg annual world-wide retail fur sales at $15 billion, almost twice what was sold in 1999.

The muskrat, whose winter pelts thicken to a deep shag, is a particularly popular low-cost fur.

"We expect muskrats to open strong this year," predicted Howard Noseworthy director of planning and development for Fur Harvesters Auction just before December's fur run. Mr. Noseworthy noted that buyers world-wide had exhausted muskrat inventory as muskrat trapping season in Michigan approached this past October.

That's when Fur Harvesters posted a notice on its website: "We are advising all trappers to start trapping muskrat the moment the season opens and target as many as possible…buyer demand is high now for rats and no stock is available."

That got trappers' attention. But some saw it as an ominous sign, a scent of irrational exuberance and the prospect of falling prices in 2012.

"The primary concern is Greece and the instability in the euro zone," says Greg Petska, a fur buyer in Ord, Neb., who operates his own fur-collection route stretching from Kansas to Oregon. "Coats are just hitting the retail shelves in Europe right now. Those coats may not sell," he warns. "The potential for monetary loss is substantial."

Other traders warn that Europe and North America are experiencing milder-than-usual winters this year, which they predict will depress fur sales. That, in turn, would damp bids for raw fur as it comes to auction in January.

Brian MacMillan, who manages fur collections for North American Fur Auctions of Wisconsin, is thinking about Kastoria—a hub of fur processing in Greece that feeds product to Russia and elsewhere in Europe.

"With the debt crisis, maybe some manufacturers won't be able to get financing," Mr. MacMillan says. In that case they would be taking fewer muskrats, which also would lower prices.

Mr. Noseworthy of Fur Harvesters says he doesn't expect the muskrat-belly market to collapse disastrously. Mr. MacMillan agrees but notes that prices for mink opened lower than expected at the recent Copenhagen auction, the first of the season.

Some trappers are hedging their bets against a belly bust. Dennis Gast, a game warden who catches muskrats in his spare time, is one of this area's most admired trappers. He brought 198 muskrats to Al Niemala's stop in Chassell, Mich., along with several raccoons and minks. But he held back his beaver pelts.

"There isn't very much upside potential on muskrats, so it's a good time to sell now," the 59-year-old Michigander explained. Beavers usually sell better in January, he added.

A drier-than-usual spring means muskrats had fewer litters this year, Mr. Gast said, which could mean fewer skins for sale this winter.

That, plus the natural aging of Michigan's trapper population could keep supply and demand in balance.

"It's just like the stock market," Mr. Gast explained, before addressing jitters over an impending muskrat meltdown: "I don't worry about it."